Directed energy deposition (DED) enables the efficient fabrication and repair of large metal components. However, repeated reuse of the powder generates degraded particles, which must be removed by sieving. This study used scanning electron microscopy and laser diffraction particle size analysis to characterize the sieve-rejected Inconel Alloy 939 powder collected sequentially after each of four DED processing cycles (R1–R4). The rejected powder consistently contained elongated, irregular, and satellite-attached particles, and its particle size increased progressively with each reuse cycle. The mean particle size increased by 16.8%, from 51.1 μm for R1 to 59.7 μm for R4. The D₁₀, D₅₀, and D₉₀ values also increased, with D90, for example, rising from 71.5 to 82.2 μm. These results suggest that sieving may serve as an important quality control step for maintaining powder quality when the powder is repeatedly reused in DED.

Due to the pandemic of SARS-CoV-2 (COVID-19) virus, the demand for personal protective equipment (PPE), including face shield, ventilator value, and so on, has abruptly increased in the world. The collapse of the global supply chain of PPE has led to a shortage of the PPE. An additive manufacturing process has emerged as one of solutions to overcome such shortage. The objective of this study was to develop a reusable protective face shield using a material extrusion (ME) process. Five types of face shield were designed. Effects of the design on effective stress distribution, deformation, and specific rigidity were investigated through finite element analyses. To examine the influence of the design on deposition and post-processing characteristics, five types of face shield were fabricated from a ME apparatus. Post-processing characteristics and building time were greatly improved when Design 1 was adopted. In addition, the overall weight, wasted material, and buy-to-fly (BTF) ratio were significantly reduced when Design 1 was applied. Finally, results of wearing and droplet spreading experiments showed that the fabricated face shield for Design 1 was applicable to protection of droplet spreading.